In 3GPP RAN LTE (3rd Generation Partnership Project Radio Access Network Long Term Evolution), OFDMA (Orthogonal Frequency Division Multiple Access) has been adopted as a downlink communication method, and SC-FDMA (Single Carrier Frequency Division Multiple Access) has been adopted as an uplink communication method.
With LTE, a radio communication base station apparatus (hereinafter abbreviated to “base station”) performs scheduling not only of downlink resources, but also of all uplink resources. That is to say, a base station transmits control information for reporting a result of allocation of uplink resources to be used for uplink data transmission by a radio communication mobile station apparatus (hereinafter abbreviated to “mobile station”) to a mobile station. Then, on receiving this control information, a mobile station transmits transmission data (uplink data) using an uplink resource indicated by the control information.
With LTE, an RS (Reference Signal) using a specific resource for each mobile station is used by a base station to obtain uplink channel information. An RS may be a DM (Demodulation) RS used for channel estimation for data demodulation, or an SRS (Sounding RS) used for channel quality estimation for frequency scheduling (see Non-Patent Document 1, for example). A DM RS is added to transmission data and transmitted at the same time as transmission data, whereas an SRS is normally transmitted over a wider band than a DM RS, independently of transmission data.
Also, with LTE, a mobile station is assumed to be provided with one antenna, and therefore a base station allocates only one SRS resource, which is an uplink resource for transmitting an SRS, to one mobile station. Here, SRS resources allocated to mobile stations are mutually orthogonal in the time domain, in the frequency domain, or in code space, and a base station can separate SRSs from mobile stations without interference. For example, when the SRSs of mobile station 1 and mobile station 2 are made orthogonal in the time domain, the base station directs mobile station 1 to transmit an SRS in slot 1 of each subframe, and directs mobile station 2 to transmit an SRS in slot 2 of each subframe.
On receiving SRSs from mobile stations, the base station performs uplink resource scheduling for each mobile station based on the relevant SRS. Also, the base station uses an SRS to generate a CQI (Channel Quality Indicator) indicating frequency domain channel quality, and decides a modulation method and coding rate (MCS: Modulation and Coding Scheme) to be used by a mobile station for uplink data based on the CQI.
Non-Patent Document 1: 3GPP TS 36.211 V8.1.0, “Physical Channels and Modulation (Release 8),” November 2007